A spark plug is conventionally used for an internal combustion engine. In general, the spark plug has a center electrode and a ground electrode to ignite an air-fuel mixture by the generation of a spark discharge within a gap between the center electrode and the ground electrode as disclosed in international Publication No. 2011/033902, Japanese Laid-Open Patent Publication No. 2009-245716, Japanese Laid-Open Patent Publication No. H09-63745 etc.
Recently, there has been a demand to increase the compression ratio of the air-fuel mixture in the internal combustion engine for the purpose of improvements in engine performance such as fuel efficiency. In such an internal combustion engine, the voltage applied to the spark plug increases with increase in compression ratio. The higher the voltage applied to the spark plug, the larger the amount of current flowing through the spark plug at the spark discharge. This leads to wear of the electrodes.
In view of the above circumstance, an advantage of the present invention is a spark plug capable of suppressing electrode wear.